The OPs description leads me to belive that the stairs should be the place to make a stand.

I would cover the stairs and have the wife (or another person) call 911. The narrow stairway becomes a fatal funnel and humans are instincively wary of attacking foes on higher ground. Psychological advantage.

This also divides the home. The police can be told that the intruder is on the first floor, and the armed homeowner and his family are upstairs.

Put a small night-lite on the bottom area of the stairs, and do not light up the top. That way, you can see down, but the intruder cannot see up as well.